The head of the Boston Public Schools system, Superintendent Carol Johnson, will retire this summer.

The head of the Boston Public Schools system, Superintendent Carol Johnson, will retire this summer.

Boston Public Schools posted the announcement on its website Wednesday morning with a video message from Johnson.

"After a long and rewarding career that I am truly proud of, I believe it is time for me to take time to focus more on family, which of course always comes first," Johnson said in the video message.

Johnson was appointed superintendent of the 57,000-student system in 2007. The announcement of her retirement highlighted that graduation rates are at their highest level in the city's history, and fall enrollment is projected to be the highest in eight years.

However, the school system has been criticized lately over issues of school assignment and its bus contractor, which has frequently delivered children late to school.

Johnson said she expects to retire in July. Her contract was set to expire in June 2015. An interim superintendent will be appointed.